The short version

The wordy-but-interesting version

Sometimes, on macOS, you run into behavior that really makes you go "huh".

An example: as you likely know, you can create a disk image with Disk Utility and format it as APFS. Which works fine.

And, if you've been reading the blog, you probably also know that APFS volumes reside in a container, which itself resides on a GUID partitioned drive. So, multiple layers: drive, partition, container, volume. You can see all those in Disk Utility.

But once you create the image, what you see in Finder is simpler: a single ejectable volume, with the name you gave it. So, you can open it, copy to it, eject it, and there you go.

Great, right?

Not so much

Ah, but programmatically, things are different.

If an application opens an image the old way, and then unmounts its volume using diskutil, umount or hdiutil, it doesn't do what it used to do.

You can easily see this in Disk Utility, too. After you create the image, try selecting the volume and clicking the eject button. When you do that, you'll see that while the volume ejected, the image is still sticking around in the sidebar. And if the image is hosted on an ejectable drive or network volume, and you then try to eject the host volume, you'll find the it can't be ejected.

Worse, if you force eject the host at this point (hey, folks—don't force eject!), you can damage the image.

Not good.

Huh.

Worlds within worlds

So, what's going on is that there are still two things "attached" from the image: the container and the partition. They don't get "released" after all the volumes are ejected for some inexplicable reason. And so, any application that mounted and ejected images can no longer rely on the previous behavior.

Mischief, managed

Fortunately, this is another situation that SuperDuper! handles for you. If you back up to an image file, you don't need to know what I've just explained: we deal with the details, and eject all the "parts" of an APFS image without any manual intervention.

As you've heard many times from me: it just works.

So while you may not want to know why, or how all this is accomplished...isn't it comforting to know that someone's figured it out and has your back?

#Finally

With that last bit of explanation, I'm happy to say that we've reached the end of this particular voyage. SuperDuper! 3.0 (release 100!) is done, and you'll find the download in the normal places, as well as in the built-in updater, for both Beta and Regular users.

SuperDuper! 3.0 has, literally, many hundreds of changes under the hood to support APFS, High Sierra and all versions of macOS from 10.9 to the present.

SuperDuper! 3.0 is the first bootable backup application to support snapshot copying on APFS, which provides an incredible extra level of safety, security and accuracy when backing up. It's super cool, entirely supported (after all, it's what Time Machine uses...and it was first overall), and totally transparent to the user.

It doesn't stop there, of course. We're already in progress on the next version, and we've got some really great things planned.

Thanks to all of you who participated in the beta, because the final release couldn't have happened without you.

And to those of you who didn't participate in the Beta: you are going to love the final result.